Influence of copolymer composition on protein adsorption and structural rearrangements at the polymer surface

Abstract

The influence of copolymer composition on protein adsorption and subsequent structural rearrangements of the adsorbed protein has been studied by (1) investigating the ability of adsorbed proteins to be displaced by proteins in solution and (2) by determining the ability of an immobilized antibody to recognize an antigen—enzyme conjugate. Surfactant-free polystyrene copolymeric latexes were used to study the effect of specific comonomers [acrylic acid (AA), methacrylic acid (MAA), 2-hydroxyethyl acrylate (HEA), and acrylamide (A)] on protein adsorption. Although the classical surface techniques of microelectrophoresis and surfactant titration could not distinguish between the different polystyrene copolymers, the extent and nature of protein adsorption were influenced substantially by the copolymer composition. Adsorption was essentially irreversible with respect to dilution but adsorbed proteins could be displaced by proteins in solution. The order of effectiveness was fibrinogen > immunoglobulin > albumin. the ability of adsorbed proteins to be displaced from surfaces followed the order PS/PHEA > PS/PAA > PS/PMAA > PS (easiest to most difficult displacement). The retention of activity of an immobilized monoclonal antibody (Phe 1.9) at the surface followed the order PS/PHEA > PS/PAA = PS/PMAA > PS (greatest to least active). Protein adsorbed to polystyrene under low protein concentrations was less readily displaced than protein adsorbed at saturating protein concentrations. Similarly, the activity of the monoclonal antibody Phe 1.9 was dependent on the final adsorbed protein concentration at the surface of polystyrene homopolymer. In contrast, the activity of Phe 1.9 immobilized on copolymer containing HEA, AA, or MAA varied little if any with the final protein concentration at the surface. The retention of activity of covalently immobilized Phe 1.9 on poly(styrene—co-chloromethylstyrene) copolymers followed the order PS/PCS/PA > PS/PCS/PHEA(3) > PC/PCS/PHEA(1) > PS/PCS/PAA > PS/PCS/PMAA = PS/PCS (greatest to least activity). Thus, the inclusion of “modifier monomers” that are hydrophilic or are capable of hydrogen bonding with proteins appears to moderate structural rearrangements of an immobilized protein reflected by both the ease of displacement from the surface and the retention of biological activity.